Browsing by Subject "Phytohormon"

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Innovative propagation techniques in banana and plantain
(2020) Opata, John; Wünsche, Jens Norbert
Despite the significant role of banana and plantain (Musa spp.) in the livelihood of millions of people mostly in developing countries and in particular Sub-Saharan Africa, cultivation of these important crops is impeded by numerous challenges. Against this backdrop, research attempts were made to improve shoot proliferation in banana and plantain by employing innovative macropropagation techniques. Banana and plantain suckers were harvested in the greenhouses of the University of Hohenheim, Stuttgart, Germany and research fields of the Crops Research Institute, Ghana. These were subjected to Plants Issus de Fragments de tige technique (PIF), which is a mechanical preparation technique. It involves paring, thus cutting off the roots of the corms with a sharp sterilized knife. Thereafter, the leaf sheaths of the corms were carefully removed, consequently exposing latent axillary buds and the apical shoot meristem. Some of the corms had the exposed meristem destroyed with crosswise incision whiles others had the meristem left intact. Various hormonal treatments with the synthetic plant hormone 6-benzylaminopurine (0, 2.25 and 225.25 mg L-1 BAP) and natural plant hormones derived from coconut water were used. Fresh and autoclaved coconut water and other additives such as papain and root growth biostimulant from seaweed were employed in various combination to treat banana and plantain corms by either soaking or vacuum infiltration. The treated corms were planted in germination beds filled with growth substrates inside growth chambers. Evaluation of solution uptake from the two application methods and subsequently effects on number and growth characteristics of lateral shoots from the treated corms were carried out. Field evaluation of growth and yield of acclimatized plantlets from the PIF technique and hormonally derived plantlets were also undertaken. The hormonal solution application method demonstrated a higher solution uptake with the method of infiltration which was about 33% more compared to the method of soaking. Results revealed an earlier shoot emergence in corms which had the apical meristem destroyed with crosswise incision, demonstrating the breakdown of apical dominance. Nonetheless, this did not contribute to significantly higher shoot numbers when compared to corms with intact apical meristem. BAP treated corms had triggered greater number of strong shoots with comparatively higher number of roots than untreated controls, however, the effect was independent of the concentration applied. The study further revealed the importance of natural growth hormones particularly the application of autoclaved coconut water as an alternative to the expensive plant growth hormone, 6-benzylaminopurine. There was a marked effect of autoclaved coconut water, resulting in earlier shoot development characterized with higher root numbers compared to corms subjected to 6-benzylaminopurine and the PIF technique, respectively. Moreover, the addition of the proteolytic enzyme papain and the root growth biostimulant seaweed extract to coconut water did not influence the growth performance of the treated corms. Vegetative growth performance, specifically pseudostem length of the main crop, was significantly influenced by the treatment at 6 and 9 months of growth in the field. BAP and seaweed extract recorded the highest numbers of suckers. Uniformity of acclimatized plantlets with well-developed roots and active leaves at the nursery stage might have contributed immensely for the uniform vegetative growth. Treating the corms with BAP and seaweed significantly influenced the bunch weight of the main crop resulting in a bunch weight of about 11 kg. However, there was no significant difference among treatments regarding bunch weight of the first sucker crop with each treatment recording a bunch weight of 11 kg.
Micronutrients, silicon and biostimulants as cold stress protectants in maize
(2020) Moradtalab, Narges; Streck, Thilo
Mitigation of abiotic stress in crops is a feature attributed to various so-called biostimulants based on plant growth-promoting microorganisms (PGPMs) plant-, compost- and seaweed extracts, protein hydrolylates, chitosan derivatives etc. but also to mineral nutrients with protective functions, such as zinc (Zn), manganese (Mn), boron (B), calcium (Ca) and silicon (Si), recommended as stress protectants in commercial formulations. This study focussed on the effects of selected biostimulants on cold stress mitigation during early growth in maize, as a major stress factor for cultivation of tropical and subtropical crops in temperate climates. Chilling stress and micronutrient supplementation Chilling stress, induced by moderately low soil temperatures (8-14°C) in a controlled root cooling system, was associated with inhibition of shoot growth, oxidative leaf damage (chlorosis, necrosis accumulation of stress anthocyanins) and a massive decline in root length (Chapter 4 and 5). Due to inhibition of root growth, nutrient acquisition in general was impaired. However, nutrient deficiencies were recorded particularly for the micronutrients zinc (Zn) and manganese (Mn). The impaired Zn and Mn status was obviously related with the observed limitations in plant performance, which were reverted by exogenous Zn and Mn supplementation (0.5 mg plant-1), finally leading to restored nutrient acquisition and improved plant recovery after termination of the cold stress period. Zinc and manganese deficiency was mainly related with impaired uptake of the micronutrients, since the cold stress-induced deficiency symptoms persisted even in hydroponic culture when all nutrients were freely available. Beneficial effects of Zn/Mn supplementation were only detectable when the micronutrients were supplied prior to the onset of the stress period via seed soaking, seed dressing or fertigation, when uptake and internal translocation was still possible. A transcriptome analysis of the shoot tissue (Chapter 5) revealed 1400 differentially expressed transcripts (DETs) after 7-days exposure of maize seedlings to chilling stress of 12°C, mostly associated with down-regulation of selected functional categories (BINs), related with photosynthesis, synthesis of amino acids, lipids and cell wall precursors, transport of mineral nutrients (N, P, K,), metal handling and synthesis of growth hormones (auxins, gibberellic acid) but also of jasmonic (JA) and salicylic acids (SA) involved in stress adaptations. In accordance with the impaired micronutrient status and oxidative leaf damage in response to the cold stress treatments, downregulation was also recorded for transcripts related with oxidative stress defence (superoxide dismutases SOD, catalase, peroxidases POD, synthesis of phenylpropanoids and lignification), particularly dependent on the supply of micronutrients as co-factors. Upregulation was recorded for BINs related with degradation of lipids, of cell wall precursors, synthesis of waxes and certain flavonoids and of stress hormones, such as abscisic acid (ABA) and ethylene but degradation of growth-promoting cytokinins (CK). Accordingly, supplementation of Zn and Mn increased the accumulation of anthocyanins and antioxidants, the activities of superoxide dismutase and peroxidases, associated with reduced ROS accumulation (H2O2), mitigation of oxidative leaf damage and improved plant recovery at the end of the cold stress period (Chapter 5 and 6). Effects of seaweed extracts Cold-protective properties similar to Zn/Mn supplementation, associated with an improved Zn/Mn-nutritional status and reduced oxidative damage, were recorded also after fertigation with seaweed extracts prior to the onset of the stress treatments (Chapter 4). However, this effect was detectable only with seaweed extract formulations rich in Zn/Mn (Algavyt+Zn/Mn; Algafect; 6-70 mg kg DM-1) but not with a more highly purified formulation (Superfifty) without detectable micronutrient contents. This finding suggests that the cold-protective effect by soil application of seaweed extracts is based on an improved micronutrient supply and not to an elicitor effect, frequently reported in the literature for stress-protective functions after foliar application of seaweed extracts. Silicon fertilization Similar to seaweed extracts, also silicon (Si), applied by seed soaking or fertigation with silicic acid, mimicked the cold-protective effects of Zn/Mn supplementation in maize seedlings (Chapter 5). The Zn/Mn status of the Si-treated plants was improved although, in this case no additional micronutrient supply was involved. However, Si application significantly reduced leaching losses of Zn/and Mn by 50-70%, as a consequence of cold stress-induced membrane damage in germinating maize seeds and favoured the root to shoot translocation of Zn. This was associated with a restoration of gene expression, similar to the profiles recorded for unstressed control plants. However, the expression of genes related with synthesis and signal transduction of ABA, as central regulator of adaptive cold stress responses in plants, was even more strongly upregulated than in the cold-stressed controls. Accordingly, expression of cold stress adaptations involved in oxidative stress defence (SOD, peroxidases, phenolics, antioxidants) and the reduction of oxidative leaf damage and improved plant recovery were similar to the plants with Zn/Mn supplementation. Plant growth promoting microorganisms Cold-protective functions were recorded also for selected microbial inoculants (Chapter 6). However, out of five tested inoculant formulations, based on strains of Pseudomonas sp., DSMZ13134, Bacillus amyloliquefaciens FZB42, Bacillus atrophaeus ABI05, Penicillium sp. PK112 (BFOD) and a consortium of Trichoderma harzianum OMG16 and five Bacillus strains (Combi-A), a significant protective effect was detectable only for Penicillium sp. and particularly for CombiA. The CombiA consortium significantly increased root length and reduced oxidative leaf damage of cold-stressed plants, associated with increased SOD and POD activities and accumulation of phenolics and antioxidants. Root growth stimulation was related with increased IAA (indole acetic acid) tissue contents and increased expression of genes involved in IAA biosynthesis (ZmTSA) transport (ZmPIN1A) and perception (ZmAFR12). The tissue concentrations of ABA were not affected by the microbial inoculants, but the shoot concentrations of JA and SA increased, suggesting an effect by induced systemic resistance (ISR). Moreover, root concentrations of cytokinins (CKs) as ABA antagonists and expression of IPT genes involved in CK biosynthesis declined, leading to an increased ABA/cytokinin ratio and accordingly to increased expression of ABA responsive genes (ZmABF2). These findings suggest that CombiA mainly acted via improvement of root growth and nutrient acquisition by activation of the plant auxin metabolism and activation of cold protective metabolic responses by induction of ISR via JA/SA signalling and ABA-mediated responses, due to inhibition of CK biosynthesis. Synergistic interactions While the different cold-stress protectants investigated in this study induced similar protective plant responses, synergistic effects were obtained by combined applications (Chapter 6). The combination of CombiA inoculation with Zn/Mn supplementation further increased the plant micronutrient status and the cold-protective effects of CombiA. For all treatments, generally the expression of cold-protective effects was further improved by use of DMPP-stabilized ammonium fertilizers instead of nitrate fertilization. Ammonium fertilization promoted micronutrient acquisition via root-induced rhizosphere acidification, increased the ABA shoot concentrations with a moderate activation of metabolic cold stress responses and stimulated root colonization of Trichoderma harzianum OMG16 (CombiA). Field performance A comparative evaluation of the various cold protectants under field conditions with stabilized ammonium starter fertilization, revealed a severely reduced seedling emergence at six weeks after sowing (44%) due to extremely cold and wet soil conditions by the end of April in 2016, associated with a low Zn-nutritional status (32 mg kg-1 shoot DM). Significant improvements were recorded particularly for starter treatments including Zn/Mn seed dressing (emergence 56%) or seed priming with K2SiO4 (emergence 72%) and also by inoculation with the fungal PGPM strain Penicillium sp. BFOD (emergence 49%) associated with a doubling of the Zn tissue concentrations. Even after re-sowing, a significant yield increase for silo maize was recorded exclusively for the K2SiO4 treatment (Chapter 5). Taken together, the findings suggest that exploitation of synergistic interactions by combined starter applications of protective nutrients with selected biostimulants, could offer a cost-effective option for cold-stress prophylaxis in sensitive crops.
Transcriptomics and hormonal regulation of cluster root development in phosphate-deficient white lupin
(2014) Wang, Zhengrui; Neumann, Günter
Among crops, white lupin (Lupinus albus) represents the extraordinary ability to acquire sparingly soluble soil phosphate (Pi) by formation of cluster roots (CRs), mediating intense exudation of phosphorus (P)-mobilising root exudates (citrate, phenolics, protons and acid phosphatase). It is widely used as a model plant for investigations of P acquisition by root-induced chemical modifications of the rhizosphere. During the last two decades, a large pool of information on CR function and physiology was obtained mainly by hypothesis-driven research. Based on these findings, this study was designed to get a more comprehensive picture of the metabolic changes during CR development using a transcriptome sequencing approach. The outcome of the transcriptome analysis was the basis for the formulation of research questions on the regulation of CR formation and function to be investigated more in detail: Chapter I, focuses on transcriptome sequencing used for the first time for a systematic comparison of different stages in CR development. To get insights into the regulatory factors involved in CR formation, special emphasis was placed on hormone-related genes. Initiation of CR primordia in the pre-emergent (PE) zone was reflected by strongest expression of genes involved in transport and biosynthesis of auxins, brassinosteroids (BRs) and cytokinin receptors. Cluster root maturation, involving meristem degeneration and root hair proliferation was associated with strongly increased expression of ethylene-related transcripts and decreased expression of auxin- and BR-related genes. Also transcripts related with abscisic and jasmonic acids and cytokinin degradation were up-regulated in mature (MA) clusters. The primary metabolism, highly expressed in juvenile (JU) clusters, underwent significant modifications during CR maturation with increased contribution of Pi-independent bypass reactions, promoting biosynthesis of organic acids. Citrate catabolism and respiration were down-regulated, triggering citrate accumulation in MA clusters. Up-regulation of phenylpropanoid pathways reflected accumulation of phenolics. Increased expression of transcripts encoding ALMT and MATE transporters may be involved in the exudation of flavonoids and citrate, while up-regulation of transcripts encoding Pi transporters mediates subsequent uptake of mobilised Pi. Predominant expression of nucleotide degradation and secretory acid phosphatase in MA clusters coincides with Pi re-translocation and mobilisation of organic soil P. Up-regulation of the FIT transcription factor, usually mediating the expression of Fe deficiency responses (root hair proliferation, proton extrusion, Fe(III)-reduction, exudation of phenolics) can be observed also in MA clusters of P-deficient Lupinus albus even under Fe-sufficient conditions. This raises the question, whether FIT has a similar function in the regulation of P deficiency responses. Chapter II, addresses the question whether sucrose acts as a shoot-borne signal for CR formation. External sucrose amendments to P-sufficient plants, at concentrations similar to those in PE root zones of P-deficient plants, induced CR formation comparable to P-deficient plants. Palatinose (25 mM), and combined application of glucose/fructose (both at 12.5 mM) failed to induce CR formation under P-sufficient conditions, demonstrating a specific signal function of sucrose and excluding osmotic and carbon source effects. However, CRs induced by sucrose were not functional with respect to citrate exudation, acid phosphatase and phosphoenolpyruvate carboxylase (PEPC) activities and expression of related genes (LaMATE, LaSAP and LaPEPC) quantified by RT-qPCR. In Chapter III, the interactions of different phytohormones and sucrose on CR formation were investigated more in detail by an integrated approach of RT-qPCR, hormone translocation analyses and exogenous application of hormones or hormone antagonists. Shoot-to-root translocation of auxin was unaffected by P limitation, supporting the hypothesis that sucrose, rather than auxins, acts as major shoot-borne signal, triggering the induction of CR primordia. Ethylene may act as mediator of the sucrose signal, as indicated by strong inhibitory effects of the ethylene antagonist CoCl2 on CR formation induced by sucrose or P limitation. As reported in other plant species, moderately increased production of ethylene and brassinosteroids (BRs) may induce biosynthesis and transport of root-borne auxins, indicated by increased expression of respective genes (YUCCA, PIN1, AUX1, BR, ACC_oxidase) in pre-emergent clusters. A role of BR in CR formation is further underlined by inhibitory effects of BR antagonists. The well-documented inhibition of root elongation by high doses of ethylene may be involved in the inhibition of lateral rootlets growth during CR maturation, indicated by a massive increase of gene expression involved in ethylene production, associated with decline of transcripts with stimulatory effects (BR- and auxin-related genes). Based on these findings, models for the regulatory networks involved in CR formation (Chapter III) and function (Chapter I) have been developed.